(1) Field of the Invention
The present invention relates to an acrylic fiber having excellent durability and dyeability, which is composed of an acrylonitrile homopolymer or acrylonitrile copolymer, and a process for the preparation thereof.
(2) Description of the Related Art
Acrylic fibers are characterized in that they are prepared by a variety of preparation processes. The reason is that the starting polymer includes not only acrylonitrile homopolymers but also acrylonitrile copolymers comprising comonomers such as acrylamide, acrylic acid, sodium acrylate, styrene, sodium sulfonate, methyl acrylate, vinyl acetate, vinyl chloride and vinylidene chloride; that there are present many solvents, for example, inorganic solvents such as an aqueous solution of a rhodanate, an aqueous solution of zinc chloride and nitric acid and organic solvents such as dimethylformamide, dimethylacetamide and dimethylsulfoxide; and further that, in case of the wet spinning method, there are present a variety of aqueous and non-aqueous coagulants.
In the ordinary wet spinning method, for industrial reasons, for example, in view of spinnability and productivity, the composition of a coagulating bath is generally set so that a spinning dope is promptly coagulated in the coagulating bath. However, where a fiber is prepared by using such a coagulating bath, because of the strong coagulating force of the coagulating bath, a dense and hard skin layer having a thickness of about 0.1 .mu.m to several .mu.m is formed on the surface of the fiber and voids are formed in the interior. This skin layer inhibits dispersion of a dye at the dyeing step and it is considered that this skin layer will cause reduction of the physical properties of the fiber, such as softness. Furthermore, the presence of voids often results in defects of the physical properties, such as occurrence of a devitrification phenomenon, reduction of the dyeability, lack of softness and reduction of the durability. The skin layer and voids seemingly disappear if the fiber is subjected to post-treatment such as drawing and heat-treatment.
Acrylic fibers can be dyed with cationic dyes, and show an excellent durability and sharp dyeability. By dint of these characteristics, acrylic fibers are broadly used as curtains and carpets in the interior decorative field, as blankets in the field of bedding and as knitted articles and jersey cloths in the field of clothing.
With recent diversification of consumer's needs, development of acrylic fibers having a much improved durability and a deeper and better dyeability is eagerly desired.